Optimizing React Component Rendering: A Deep Dive into useMemo

Payoda Technology Inc
4 min readJul 13, 2023

In modern web development, building performant and efficient user interfaces is crucial. Component rendering plays a vital role in achieving these goals. React, a popular JavaScript library provides two powerful tools for optimizing rendering in functional components: useMemo and memo. This blog post will explore these concepts, understand how they enhance performance, and learn when and how to use them effectively.

Understanding Component Rendering

Rendering is the process of transforming data into a user interface. In React, components are the building blocks of the User Interface. When a component’s state or props change, React re-renders the component and its child components. However, unnecessary re-renders can impact performance. To avoid this, we can optimize rendering using useMemo and memo.

Enhancing Performance with useMemo

The React useMemo hook helps memoize a function’s result and runs when there is an update to one of its dependencies. It allows us to store the computed value and retrieve it when needed instead of recomputing it on every render. By doing so, we can optimize expensive computations or complex operations, ensuring they are executed only when necessary. We will experience, after proper experiments, where useMemo can be beneficial, such as processing large datasets or performing complex calculations within a component.

Preventing Unnecessary Re-renders with memo

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Image by storyset on Freepik

The memo higher-order component (HOC) is another optimization tool React provides. It allows us to memoize the rendering of a functional component based on its props. React skips the rendering process and reuses the previously rendered result if the component receives the same props. This technique can significantly reduce unnecessary re-renders and enhance performance when components have expensive rendering processes or depend on static data.

The Major Differences Between React.memo() and useMemo()

1. Purpose: React.memo() is primarily used to optimize the rendering of components, while useMemo() is used to optimize specific function calculations or computations within a component.

2. Usage: React.memo() is a higher-order component (HOC) that wraps around a component, whereas useMemo() is a hook that can be used inside a functional component.

3. Memoization: React.memo() memoizes the rendered output of a component based on the equality of its props. It prevents unnecessary re-renders by reusing the memoized result when the props remain the same. On the other hand, useMemo() memoizes the result of a function call and returns the memoized result when the dependencies (inputs) provided to it remain the same.

4. Granularity: React.memo() optimizes the rendering of an entire component. If the props passed to the component remain the same, the component is not re-rendered. useMemo(), on the other hand, allows you to optimize specific functions within a component by memoizing their results based on the dependencies provided.

5. Performance Impact: React.memo() can significantly improve performance by preventing unnecessary re-renders of components. It reduces the rendering time and avoids expensive calculations. useMemo() helps optimize function calculations by memoizing the results, thus avoiding unnecessary re-computations. It can improve the performance of components that have computationally expensive function calls.

Know More,
Performance Optimization Aspects and Techniques in ReactJS

When to Use useMemo()?

Use useMemo when you have expensive computations or data transformations within a component. By memoizing the result, you can avoid recomputing it on every render. This is especially useful when dealing with large datasets, complex calculations, or custom data transformations. However, remember that using useMemo for every value can decrease performance, so only apply it when necessary.

When to Use React.memo()?

Use a memo to prevent unnecessary re-renders of a functional component. This is beneficial when the component’s rendering process is expensive or depends on static or rarely changing props. However, be cautious with memoizing all components, as it might hinder the flexibility of React’s rendering system. Apply memo selectively to optimize specific components where performance gains are noticeable.

Here’s a sample of checking previous and next props and rendering components based on the required condition.

const propsAreEqual = (prevProps, nextProps) => {
return prevProps.userName === nextProps. userName ;
};

export default connect()(React.memo(MyComponent, propsAreEqual));

In this example, only when there is a change in the userName prop specific to this MyComponent will MyComponent re-render.

Wrapping Up

Optimizing component rendering is essential for building performant and efficient React applications. The useMemo and memo features provided by React offer powerful tools to achieve this optimization in functional components. By leveraging useMemo for expensive computations and memos to prevent unnecessary re-renders, we can significantly enhance the performance of our applications.

If you’d like to have an expert consultation on the these tools judiciously, and know more about applying them where the benefits outweigh the potential drawbacks and measuring the impact on your specific use cases, feel free to talk to us.

Authored by: Starlin Daniel Raj

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Payoda Technology Inc

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